4.18 sdds::Writer creation and append modes

• name:
  Writer::create, Writer::toStdout, Writer::toSink, Writer::append, Writer::appendToLastPage
• description:
  Create a move-only streaming writer, append complete pages to an existing file, or reopen its final page for incremental updates. A new writer owns a validated copy of the output layout.
• synopsis:
  static sdds::Writer create(const std::filesystem::path &path,  
                             sdds::Layout layout,  
                             sdds::WriterOptions options = {});  
  static sdds::Writer toStdout(sdds::Layout layout,  
                               sdds::WriterOptions options = {});  
  static sdds::Writer toSink(std::unique_ptr<sdds::OutputSink> sink,  
                             sdds::Layout layout,  
                             std::string sinkName = {},  
                             sdds::WriterOptions options = {});  
  static sdds::Writer append(const std::filesystem::path &path,  
                             sdds::WriterOptions options = {});  
  static sdds::Writer appendToLastPage(const std::filesystem::path &path,  
                                       std::int64_t updateInterval,  
                                       sdds::WriterOptions options = {});

• arguments:
  • path — New or existing output path.
  • layout — Validated output layout.
  • sink — Owned output sink.
  • sinkName — Name used in diagnostic context.
  • updateInterval — Row-count publication interval for a live page.
  • options — Per-writer configuration.
• return value:
  An open, move-only sdds::Writer. layout() returns its immutable output layout and rowsPresent() reports rows staged or present during an update.
• exceptions:
  sdds::IoError, sdds::FormatError, or sdds::StateError for file, layout, locking, append, or update incompatibilities.
• see also:
  Sections 4.17, 4.19, and 4.20.